a Flat note is what most bass lines in rock and some in rap are...i dont know exact frequincies but one octave of notes is a double in Hz...the 1st octave is 20-40Hz...the notes are 20, 20.5, 25, 27.5, 30, 32.5, 35, 37.5, and 40Hz...flats in the 1st octave are extremely hard to tell from notes...notes are combined to make harmonis...our hears like htoes harmonics...flats our ears only like alone and are the easyest to re create....low flats are hard to hear ad decent listening levels...